Power generation facilities such as solar photovoltaics and wind turbines vary in output power in accordance with conditions in the natural environment. When use of these renewable energy facilities is increased, there is a need for power stations such as conventional thermal power and water power stations to be able to absorb a variation in the output of the renewable energy facility. For example, a pumped-storage power station which has been operated to adjust for variation in the daily electric power demand (relatively long term change) is requested to function not just for long-term adjustment but also short-term adjustment.
However, the operation is switched from pumping to power generating or from power generating to pumping as necessary in order to realize input/output adjustment in a pumped-storage power generation facility. Therefore, there is a problem in that operation of the facility should be stopped and then restarted, which takes time.
Under the circumstances, it is desired to provide a technique for switching the pumping operation (power consumption) and the power generating operation (power supply) without stopping the pumped-storage power generation facility.